Hexachrome

http://en.wikipedia.org/wiki/Hexachrome

Hexachrome is Pantone's six-color color printing process. In addition to custom CMYK inks, Hexachrome adds orange and green inks to expand the color gamut, for better color reproduction. It is therefore also referred as the CMYKOG process.

Some printers use lighter CMYK "photographic dye" with identical hue, e.g. the "CcMmYK" process, but for a different purpose. These ink sets provide smoother blends, particularly in areas with low saturation. They do not, however, extend the limits of the color gamut of the device, which is still constrained by the cyan, magenta, yellow, and black inks.

Some inkjet printers have incorporated the same concept of extended gamuts, including printers from Canon (Orange and Green) and MacDermid Colorspan (Blue, Orange, Red, and Green, for a CcMmYyKkBORG configuration).

While the details of Hexachrome are not secret, use of Hexachrome is limited, by trademark and patent, to those obtaining a license from Pantone.

Typically, software that works with Hexachrome does not require a designer to specify the amounts of each ink. Instead the designer uses RGB colors tagged with a specific ICC profile, and as part of raster image processing this is converted using a six-channel ICC profile provided by Pantone.

CMYK

http://en.wikipedia.org/wiki/CMYK_color_model

CMYK (short for cyan, magenta, yellow, and key (black), and often referred to as process color or four color) is a subtractive color model, used in color printing, also used to describe the printing process itself. Though it varies by print house, press operator, press manufacturer and press run, ink is typically applied in the order of the acronym.

The CMYK model works by partially or entirely masking certain colors on the typically white background (that is, absorbing particular wavelengths of light). Such a model is called subtractive because inks “subtract” brightness from white.

In additive color models such as RGB, white is the “additive” combination of all primary colored lights, while black is the absence of light. In the CMYK model, it is just the opposite: white is the natural color of the paper or other background, while black results from a full combination of colored inks. To save money on ink, and to produce deeper black tones, unsaturated and dark colors are produced by substituting black ink for the combination of cyan, magenta and yellow.